Charge air within the meaning of the invention shall be understood as compressed air, compressed by an exhaust turbocharger or any other kind of charger.
For turbocharged engines, geometry (diameter and length) of charge air ducts (also called charge air delivery ducts) is tuned to take benefits from pressure waves for improving the air filling into the engine cylinders, and thus performance.
However, optimal geometry of charge air ducts is dependent on engine speed. At low engine speeds, for instance below around 2000 rpm (revolutions per minute), and high load, the turbocharger compresses the supplied air in an effective manner. Under these engine operating conditions, a charge air duct of small length and larger diameter is suitable in order to reduce pressure loss and increase the engine power.
At low engine speeds (around 1250 rpm for instance) and part load operation, the turbocharger compressor is not very effective (the charging effect of the turbocharger is poor and limits the engine output torque). Under these engine operating conditions, a longer duct having a reduced inlet diameter is appropriate in order to increase the engine feeding (i.e. the mass of gas introduced into the combustion chamber) and thus the volumetric efficiency.
Conventional charge air ducts have a fixed length, which is a trade off between engine torque and power. With a charge air duct of fixed length, the engine performance is optimized at a specific engine speed, but not on a large operating range. Also, because of harsh environmental requirements in the automotive sector, aiming to reduce fuel consumption and CO2 emissions, there is a great demand for increase in the engine output torque of a turbocharged engine in the low engine speed range.
Therefore it is desirable for optimal engine control to have the possibility to change the air inlet of a combustion engine between different air duct branches according to engine speed and load condition.
DE10314629A1 discloses an induction system for an internal combustion engine which has a rotary valve directing the incoming fuel/air mixture either through a short wide induction pipe or a narrow long induction pipe. The fuel/air mixture passes through an inlet channel into a chamber with several short wide tubes and long narrow tubes leading to the individual cylinders. A rotary valve body forms part of a valve assembly and is accommodated in a cylindrical housing. The housing has a wide opening for each cylinder and a narrow opening. The valve body is rotated to line up wide or narrow passages with the entry port for each cylinder.